dmaengine: ti: k3-udma: Use struct_size() in kzalloc()

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

This code was detected with the help of Coccinelle and, audited and
fixed manually.
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Addresses-KSPP-ID: https://github.com/KSPP/linux/issues/83
Link: https://lore.kernel.org/r/20200619224334.GA7857@embeddedorSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/ti/k3-udma.c

@@ -2171,7 +2171,7 @@ udma_prep_slave_sg_pkt(struct udma_chan *uc, struct scatterlist *sgl,
 	u32 ring_id;
 	unsigned int i;
 
-	d = kzalloc(sizeof(*d) + sglen * sizeof(d->hwdesc[0]), GFP_NOWAIT);
+	d = kzalloc(struct_size(d, hwdesc, sglen), GFP_NOWAIT);
 	if (!d)
 		return NULL;
 
@@ -2487,7 +2487,7 @@ udma_prep_dma_cyclic_pkt(struct udma_chan *uc, dma_addr_t buf_addr,
 	if (period_len >= SZ_4M)
 		return NULL;
 
-	d = kzalloc(sizeof(*d) + periods * sizeof(d->hwdesc[0]), GFP_NOWAIT);
+	d = kzalloc(struct_size(d, hwdesc, periods), GFP_NOWAIT);
 	if (!d)
 		return NULL;